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The National Research Council has released a report on the search for alien life forms that warns -- rightly, in my view -- against "Terran" thinking. Terran, or Earth-based thinking, is the kind of necessarily blinkered expectation that takes only the Earth as its model. Life out there, Terran thinking assumes, looks roughly like life here, perhaps with some fanciful variations. When H.G. Wells...

The National Research Council has released a report on the search for alien life forms that warns -- rightly, in my view -- against "Terran" thinking. Terran, or Earth-based thinking, is the kind of necessarily blinkered expectation that takes only the Earth as its model. Life out there, Terran thinking assumes, looks roughly like life here, perhaps with some fanciful variations. When H.G. Wells wanted to imagine sentient Martians he essentially made them great big octopi -- a better move than handsome people in silver jumpsuits, but just as provincial.

I spoke with one of the NRC panel members, Steve Benner, recently in the course of researching an article on the RNA World hypothesis -- the suggestion that RNA predates DNA, and was once the only chemical coding system on the planet. Benner is a terrifically fun person, and has that condition someone once used to describe Murray Gell-Mann: "He has three brains, and each of them is faster than yours." He's also doing amazing things: the Benner lab pioneers a field called "synthetic biology‚" which is just what it sounds like. They have already synthesized an expanded DNA alphabet that generates its own proteins as well as self-replicating molecular systems that undergo chemical evolution . . . on their own. When I asked him how this was different from creating life in a test tube, he laughingly said, "If I called it that, I wouldn't get funding."

image: Peter Kaminski

At the time I spoke with him Benner had already been commissioned to write up a series of NASA Astrobiology Institute guidelines on "what to look for when looking for aliens" -- our most far-reaching guesses at what galactic biosignatures might look like. In those as well as the current NRC report, he underscores the real possibility that we might travel all those millions of miles and miss the prize because it doesn't occur to our robotic probes that, say, the ammonia-rich ice crystals they're rolling over might be alive.

Could we really meet ET without knowing it? I'm going to hazard a guess here and suggest that it"s very unlikely we *would* know it, at least at a first pass. (Even life on Earth is far more diverse, and frankly weird, than most people imagine.) The Martian meteorite ALH 84001 gives an excellent example. It looked to some people like microfossils. Others said no, these were simple geological formations. The latter view has won out, barring dramatic new data. But the whole tenor of the discussion encapsulates the problem: are we looking at living things or not?

image: beachy

And that's a relatively simple case. Presumably, the farther we go from microbes, the more complex the problem. One of the many strengths of Stanley Kubrick's 2001: A Space Odyssey is the out-and-out weirdness of the stargate sequence: what on earth are we looking at? Is this machinery, natural phenomena, a hallucination, a dream? All attempts to read the sequence literally are bizarrely frustrated, throwing us up against that realization that it can't be understood in the terms we are used to applying. The film compellingly replicates, at least for me, the experience that I imagine awaits us when we actually encounter sentient technological civilization: a big part of the challenge is going to be just figuring out what is happening.

At a lower-brow level, when you bring up the question of defining life at parties someone invariably mentions the Horta, a silicon-based organism from the original Star Trek series that looks a lot like an extra underneath a rug. This rocky critter shuffled around with an eerie scraping sound, suggesting it was midway between a huge amoeba and a pile of bricks. Could life really be based on silicon? I ran this question past a panel of SETI researchers at a Harvard conference two years ago and the response was actually pretty skeptical: don't rule it out, but, as one panel member said, the biproduct of cellular respiration is carbon dioxide. What's another name for silicon dioxide? Sand.

The point is double: it's hard to imagine how sand could be part of an active, metabolizing system. It seems the very definition of inert. Second point: who knows? So far we have an N of 1 regarding life blueprints: carbon-based, water-solvent, DNA-coded, and more or less smooshy. But does any living thing have to meet these requirements? If we write silicon life out of the definition a priori, you can be guaranteed we won't ever find it.

Other possibilities: life that uses methane as a solvent (Titan, anyone?), life that uses RNA instead of DNA (Benner and others speculate that RNA-based life might even still be present on Earth, in super-remote locations such as under the ocean floor), life that uses some as-yet undiscovered coding mechanism; life in a gaseous form. No one to my knowledge has suggested plasma-based life, though it appears in David Brin's novel Sundiver and, actually, in Arthur C. Clarke's original Space Odyssey, a much more literal sci-fi treatment than its famous film version. Our stargate-hopping hero witnesses a permanent solar flare he suspects of sentience. I personally can't help but think of the alien zoo in Stanley Kubricks's earlier film Dark Star that includes, among other organisms, a species that seems to be nothing more than a hovering cloud of lights.

Is that absurd? If nature has shown herself to be anything, it's resourceful. When we do succeed in finding, and recognizing, life out there, the aliens of popular imagination will no doubt seem the most absurd suggestion of all.

Temporal problems too. Earth's day, year, and gravity are not likely to be duplicated. Do we recognize a species to whom we look like hummingbirds on speed? Human temporal experience is not shared even with other species here.

The most important factor in life-form existence, has to be environment?

You would not expect find Human-Beings walking around on the ocean floor near the mid-atlantic ridge? and like wise you would not expect the species that benefit from the thermal vent hotspots deep in the ocean, to be able to adapt to the climate of the Antartic?

It is the environment that shapes the species.

Rna, in chemical structure form would have been a direct result from the Earths environment many eons ago, if one takes the current environment now (inside the human body), then one can make calculations as to the suitability of Rna over Dna, calibrated from the other components that provide the most suitable environment for the existence of life giving compounds.

I would expect (your posting seems to indicate) if one synthesize's a large number of different molecular environments, and oserve which solutions provide the "best" for Dna survivability, one can deduce that this would be comparable to the actual evolution of the Earth's chemical history, and thus, one can produce subtle changes as observe where life thrives, and where it gets instantly wiped out?

Getting life to "exist" over a long period of time is the tricky part, a perfect environment may have taken eons to occur, and a suitable sustainable environment can be maintained only with small subltle changes, rather than rapid changes.

WRT the 2001 "space oddity" ? stargate sequence, I have always seen it as a time-travel, faster than light speed, that takes Bowman "into his future", where he meets the "older" Bowman/himself?..and of course the opening sequence of 2001 is about the very thing of changing environments?..the apes are quite happy to go about their existence without any friction to each other, then change occurs as a "new" electro-magnetic resonating obilisk appears, and they investigate it's appearence by approaching and touching. This experience quite litirally "shocks" the apes and instigates thought?..then into other local things such as "bones"..the experience of "rain".."lightening"..and everything else they previously ignored!..the rest is as I'm sure you know is "History"!

The film has a layered content, relating to "change" in environments, cause and effect?

An interesting example of this right here on earth is the so-called nanobacteria (sometimes spelled nannobacteria). These are small particles, less than 100 nm, found in various organic and inorganic media which bear some resemblance to bacteria. Some researchers claim to have seen them reproduce in culture and show other signs of being alive. However they are too small to be "life as we know it", too small to hold DNA, ribosomes and the related molecular machinery that we understand as part of life, hence mainstream biology rejects the notion that they are living entities. The experimental data is inconclusive but it looks to me like much of the skepticism is based on the theoretical impossibility of such small organisms rather than hard evidence. This attitude betrays a set of strong assumptions about the nature of life.

I must just say, is it not still somewhat "terran" to assume DNA or RNA as the most likely nucleic acids? There exists on Earth, for instance, PNA - peptide nucleic acid. Essentially RNA without a sugar phosphate backbone.

Indeed, aside from the question of cosmic abundance, why even carbon? Many properties of carbon are shared with other non-metallic elements, notably sulphur and phosphorus. These are often dismissed due to their "high reactivity", but chemical reactivity is a relative concept -- largely a question of kinetics. After all, even water is flammable if kept in a fluorine atmosphere...

I've sometimes wondered whether or not we would be able to recognize sentience in another lifeform and, conversely, whether our civilization would be recognizable as a product of sentience if it were examimed through the lens of a truly alien intelligence.

Consider that to an untrained eye, an anthill looks pretty chaotic. If we could see the pheromone trails, we would recognize a great deal more structure associated with the colony. If we could watch the evolution of the trail networks over a sufficiently long span of time, we would begin to see the colony as a single entity rather than a collection of ants. Now consider how difficult it is for most people to learn to see the ant colony from the latter perspective.

Things are even more problematic if you consider the fact that information is conserved (according to the known laws of physics). So, one could argue that we also exist in the early universe (but we would still subjectively perceive ourselves to be alive in the universe as it is today).